DESCRIPTION (Adapted for the Applicant's Abstract): The proposed research will focus on vaso-occlusive mechanisms in sickle cell anemia, emphasizing the role of erthrocytic and vascular factors. In particular, a better understanding of the integrated physiology in vivo mechanisms is required to devise effective therapies. The overall hypothesis is that in sickle cell anemia, reversible sickling in vivo results in pleiotropic effects such as red cell heterogeneity, endothelial injury, red cell-endothelial interactions, and altered vascular responses. These abnormalities will then contribute to vasoocclusive crisis and multiple organ damage. The Applicant will use a transgenic mouse model expressing human, alpha, betaS, betaS- Antilles globins on the mouse homozygous Beta-major deletional background. This model meets the basic requirements necessary to test the above hypothesis, such as the presence of red cell heterogeneity, intravascular sickling, red cell adhesion and chronic, multiple organ damage. In vivo studies in the sickle transgenic mouse will be complemented by selected experiments with human SS cells in ex vivo systems. In the transgenic mouse, they will test the hypothesis that the above pathological manifestations are a direct consequence of intravascular sickling. The proposed in vivo studies will elucidate: i) microrheologic correlates of microvascular abnormalities; ii) the role of cytokinase and NO; iii) and mechanisms of altered microvascular responses. The proposed experiments with human SS cells are driven by our novel findings that show involvement of band 3 protein in adhesion using ex vivo mesocecum vasculature as well as human endothelial cells in a flow chamber. The results of these studies are expected to elucidate new mechanisms with relevance to the human sickle cell disease, particularly in validating the basis for certain therapeutic approaches.